1. Field of the Invention
The present invention relates generally to displacement encoders and, more particularly, to digital encoders for use with mechanical switches.
2. Related Art
A variety of conventional displacement encoders are known that produce digital signals in response to a user-supplied mechanical action. Such devices typically are used, for example, on instrument panels to allow a user to select from a number of values available for a given user input. The user-supplied mechanical action is typically provided through a knob, wheel, button, slide, lever or other mechanical actuator. Such mechanical interfaces may be provided, for example, on an instrument to allow the user to vary the value of a setting by rotating the knob or wheel, pushing the button, or displacing the slide or lever. In some such known devices, the rate of change of the setting is responsive to the rate at which the mechanical actuators are rotated, pushed, slid, or otherwise displaced from a null or nominal position. For example, a knob may be provided on an oscilloscope or defibrillator to allow a user to adjust the magnification of a displayed waveform. Generally, the user may cause the magnification to increase slowly by rotating the knob slowly, or increase rapidly by rotating the knob rapidly.
One type of conventional digital encoder is a rotary pulse generator. Rotary pulse generators provide variable-rate zooming or scrolling by allowing the user to adjust a mechanical actuator wheel on, for example, an instrument panel. The wheel is perforated with a series of slits in one or, more commonly, two rows. Two pairs of optical emitters and receivers, one pair for each row, sense the number of optical pulses resulting from the intermittent passage of light through the slits as the wheel is turned. The phase difference between the optical pulses generated by the two rows of slits indicates the direction of rotation. An electronic circuit detects and analyzes the dual pulse stream thus generated and converts this information into digital signals. The digital signals may be presented at a single output having multiple discrete voltage levels representing multiple rates of wheel rotation in each of the two directions, and one voltage level indicating that no rotation is occurring. In some conventional rotary pulse generators, the digital signals are presented at binary outputs.
The digital signals generated by digital encoders typically are provided to a controller such as a microprocessor, a general purpose computer, or the like. The controller converts the digital signals into appropriate control signals for changing the value associated with the user input. For example, in the conventional magnification adjustment wheel introduced above, a slow rate of rotation of the wheel in one direction may cause the controller to slowly increment the associated magnification value by increasing that value""s least significant digit. A more rapid rotation in the same direction may cause the controller to more rapidly increase the magnification value by increasing the next-most significant digit, and so on. Rotations in the opposite direction result in analogous decrements to the appropriate digits of the controlled value. Other types of known digital encoding devices produce digital signals that are responsive to the degree, rather than the rate, of motion. For example, a user may rotate a knob mechanically coupled to a rheostat, thereby producing an analog voltage that varies in proportion to the extent to which the knob is rotated. Any of a variety of known circuits including analog-to-digital converters may then be used to convert the analog voltage to digital signals. The digital signals are processed by a controller in an appropriate manner.
These and other conventional digital encoders, however, suffer from one or more of the following disadvantages. Many conventional digital encoders include numerous components. For example, the rotary pulse generator includes light emitting and sensing components and associated detection conversion circuitry. Such components add cost and complexity to the host instrumentation or other device in which the displacement encoder is implemented. Other known digital encoders require less costly or less complex components to generate analog signals, such as the above-noted rheostat. However, these digital encoders require an additional analog-to-digital conversion component that again adds cost and complexity. Moreover, in some applications, the requisite number of components necessary to implement such known digital encoders has been found to be incompatible with the limited space or dimensional requirements of the host device. Furthermore, the additional complexity may also adversely affect reliability and accuracy.
What is needed, therefore, is a system and method that provides an inexpensive, simple and reliable technique for digitally representing a position of a user-controlled mechanical actuator.
The present invention is a digital displacement encoder and associated methodology that overcomes the above and other drawbacks of conventional systems which digitally encode a user-supplied displacement. In one aspect of the invention, a digital displacement encoder is disclosed. The digital displacement encoder includes a mechanical actuator constructed and arranged to be displaced to one of a null and a plurality of activation positions in response to an externally-provided force. Also included is a conductive member constructed and arranged to be positioned to one of a plurality of intermediate positions in response to the change in position of the mechanical actuator. A contact array comprising a plurality of activation signal contacts is fixedly disposed proximate to the conductive member. Also included is a digital signal generator comprising one or more electrical circuits electrically coupled to the plurality of activation signal contacts, and one more terminals at which output signals are provided. The conductive member electrically contacts a predetermined one or more of the plurality of activation signal contacts when the mechanical actuator is in each of the plurality of positions. At each of the intermediate positions, the conducive member electrically alters the electrical circuits that include the contacted signal contacts to cause a change in output signals.
Preferably, the conductive member is comprised of a conductive elastomeric material. Also, it is preferable that a biasing element be included to urge the conductive member toward its null position. In one embodiment, the digital signal generator is a voltage pull-up circuit, although any type of circuit may be used. In one embodiment, the digital signal generator provides a plurality of output signals having a nominal state responsive to the mechanical actuator being in the null position, and a plurality of activation states each responsive to the mechanical actuator being in one of the plurality of activation positions. In certain embodiments, the conductive member is electrically connected to an activation reference voltage corresponding to an activation state of the output signals. The activation reference voltage may be at ground potential or at some supply voltage. Preferably, the signal contacts are traces on the printed circuit board. The mechanical actuator may be a rocker button, wheel or slide, among others.
In another aspect of the invention a digital displacement encoder is disclosed. The digital displacement encoder includes a signal generator circuit comprising a plurality of output terminals and a plurality of activation signal contacts each fixedly connected to a base and electrically connected to at least one of the output terminals. A mechanical actuator movably disposed with respect to the base so that it may be positioned at any of a plurality of positions in response to a user-supplied displacement. The actuator comprises a conductive member configured to be located at a null position and a plurality of activation positions, the conductive member disposed away from each of the plurality of activation signal contacts while in the null position and contacting one or more of the activation signal contacts while in each of the plurality of activation positions. The conductive member causes the signal generator circuit to generate one or more digital output signals at the output terminal(s), each the plurality of digital output signals having a first state associated with the null position and a second state associated with the activation position. In one embodiment, the digital signal generator is a voltage pull-up circuit, although any circuit now or later developed may be used. The base is preferably a printed circuit board and the signal contacts comprise traces on the printed circuit board. A biasing element is preferably included in certain embodiments to urge the conductive member toward its the null position.
In another aspect of the present invention a method for digitally encoding a plurality of user-supplied displacements of a mechanical actuator is disclosed. The method includes the steps of a) positioning a mechanical actuator to a selected one of a plurality of positions; b) electrically altering a signal encoder circuit associated with the selected position of the mechanical actuator, the signal encoder circuit including one of a plurality of signal contacts of a signal contact array; and c) generating, by the altered circuit, one or more output signals identifying the selected position of the mechanical actuator. In one embodiment, step b) comprises the step of 1) positioning a conductive member operationally coupled to the mechanical actuator to one of a plurality of intermediate positions associated with the selected position of the mechanical actuator, the conductive member contacting one or more of the signal contacts when in the intermediate position, thereby electrically altering the signal encoder circuit.
Advantageously, the digital signal encoder may be configured with any number of signal states and output terminals to achieve a desired degree of refinement to reflect the position of the mechanical actuator. Another advantage of the present invention is that it directly converts a continuous user-supplied displacement into a digital electrical signal. This capability for direct encoding is in contrast to some known systems and methods that convert continuous mechanical action into analog electrical signals, and then convert the analog electrical signals into digital electrical signals. By eliminating the need for analog-to-digital conversion, the present invention generally reduces cost and simplifies operation in comparison to such known systems and methods.
The present invention also provides significant commercial advantages over other types of known systems that provide direct digital encoding of user-supplied mechanical action. In particular, the digital displacement encoder of the present invention is generally less expensive and less complex than such known direct encoding systems and methods, and may also be more reliable and more compact. In addition, the present invention typically provides the user with superior tactile feedback as compared to known direct or indirect digital encoding systems and methods.
A still further advantage of the present invention is the use of a conductive elastomeric material, which is compliant and conductive. Such a conductive elastomeric material provides a secure electrical connection with each of the signal contacts as it comes into contact as a result of the intermediate displacement, irrespective of irregularities that may occur in the surface of signal contacts or of other factors.